GBA Logo horizontal Facebook LinkedIn Email Pinterest Twitter Instagram YouTube Icon Navigation Search Icon Main Search Icon Video Play Icon Plus Icon Minus Icon Picture icon Hamburger Icon Close Icon Sorted

Community and Q&A

Foundation Type for Passive House on Rocky Site

TJNorth | Posted in PassivHaus on

Hi, I’m considering a PassivHaus standard project up in northern Ontario.

For the foundation, I’ve looked into Frost Protected Shallow Foundation (FPSF), as well as helical piers, and the traditional full basement dig. I’m leaning toward piers just because there’s less heavy machine work involved and I like the idea of being nearly completely separated from ground freeze issues. Initial thought is to leave the area below the house open, so there are no complicated crawl space issues to deal with.

However, there are large rock formations in the area (Sudbury Basin) and it crossed my mind that if one could find a fairly smooth, large rock formation and add just enough concrete and fill to create a perfectly smooth surface, they’d be on very solid ground with no concern for frost heave. I never see this, and I have a suspicion that it is a stupid idea, but I’m not exactly sure what’s wrong with it. Anyone care to comment?  Another version would be to use piers drilled into the rock which would require no fill / concrete leveling but might be more costly than the concrete option.

GBA Prime

Join the leading community of building science experts

Become a GBA Prime member and get instant access to the latest developments in green building, research, and reports from the field.


  1. plumb_bob | | #1

    I have no experience building on bedrock and I am inherently suspicious of helical piles.
    Any sort of pier foundation will require you to insulate the floor, which creates problems for both insulation and plumbing.
    For a FPSF, you will need to build up a pad of compacted earth on top of the bedrock if you want to have plumbing run through the slab. This could get weird if the site is sloping.
    I would build an insulated ring wall foundation, partly because this is what I am familiar with, and partly because is uses standard details that work well.

  2. charlie_sullivan | | #2

    One concern with using a large flat existing rock as a foundation is that insulating would be tricky: you would need to insulate on top of it, not inside or outside the perimeter. There would be ways to do that, but it might be easier to do helical piles and deal with that insulation challenge.

Log in or create an account to post an answer.


Recent Questions and Replies

  • |
  • |
  • |
  • |